The synthesis of stable Pt nanoparticles (Pt NPs) and their attachment to glassy carbon (GC) and gold electrodes have been investigated. Two strategies have been followed, by reaction with the thiol termination of a self-assembled monolayer of 1,4-benzenedimethanethiol (BDMT) on gold and by chemical bonding through an amide linkage between the carboxylate group of 11-mercaptoundecanoic acid (MUA)-stabilized Pt NPs and aminophenyl groups grafted on a GC electrode. The functionalized substrates and the Pt NPs synthesized were characterized by reflectance adsorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy, ellipsometry, and high-resolution transmission electron microscopy (HRTEM). Their electrocatalytic properties for the oxygen reduction reaction (ORR) were investigated by rotating disk electrode measurements. It is shown that particles attached by amide bond formation from a C11 tether lead to a decrease in the ORR rate constant by a factor of approximately 5 compared with Pt NP connected to the electrode surface by phenyl group that provides a high conductivity between the substrate and the Pt particles. The ORR occurs through a four-electron transfer on both electrodes.